the shoulder hinge is NOT a replacement, it's the one that came w/ my 1S... no crack, just tiny stress marks around the fat end of the pin.
i just finished sanding down the fat end of the pin and reinserted it back... it is still pretty tight, no worries whatsoever that the pin will slip out on its own, 0% chance... tested it by closing and opening the hinge continuously many times and i even cranked it... seems fine... even the slight bulge it had near where the stress mark was and the stress mark seems to have disappeared!
... i have put as much stress on it, pulling the two parts in different directions, as much as i possibly can w/o forcibly breaking it... and its still fine.